There have been known multimode filters in which a plurality of Interdigital Transducers (IDTs) are arranged in the propagation direction of a surface acoustic wave (SAW) on a piezoelectric substrate. Longitudinally-coupled double-mode SAW (DMS: also called as Dual Mode SAW or Double Mode SAW) filters have been often used as the multimode filters. To increase the suppression in other than the passband in the DMS, it has been known to connect a plurality of DMSs in series between an input terminal and an output terminal.
Japanese Patent Application Publication No. 9-130203 describes that the pitches of electrode fingers of DMSs that are two-stage longitudinally-coupled are made to be different by 0.2% to 0.5% to reduce the group delay deviation. Japanese Patent Application Publication No. 9-214284 describes that the passband is widened by combining the passbands of the DMSs.